Conventionally, as a gland packing material which is useful in production of a gland packing, for example, known are a material disclosed in Japanese Patent Publication No. 6-27546 (hereinafter, referred to as conventional art 1), and that disclosed in Japanese Patent No. 2,583,176 (hereinafter, referred to as conventional art 2).
In conventional art 1 above, as shown in FIG. 22, an expanded graphite tape (51) is folded along longitudinal fold lines to form a cord-like member (52), and the cord-like member (52) is covered by a reinforcing member (53) configured by a knitted or braided member of metal wires such as stainless steel, inconel, or monel, thereby forming a gland packing material (50).
In conventional art 2 above, as shown in FIG. 23, a cord-like member (52) of an expanded graphite tape (51) is covered by a reinforcing member (53) configured by a knitted or braided member of metal wires, and the resulting member is folded to a V-like shape along a longitudinal fold line, thereby forming a gland packing material (50).
In both the gland packing materials (50) of the conventional art, the outside of the cord-like member (52) is reinforced by the reinforcing member (53) configured by a braided member of metal wires or the like (hereinafter, such reinforcement is referred to as external reinforcement). Therefore, the gland packing materials (50) are provided with high tensile strength. Consequently, a plurality of such gland packing materials (50) are bundled, and then subjected to a braiding or twisting process, so that a gland packing can be produced. In conventional art 1 above, when eight gland packing materials (50) are bundled and an eight-strand square-knitting process is conducted, for example, a gland packing (54) which is braided as shown in FIG. 24 is produced, and, when six gland packing materials (50) are bundled and a twisting process is conducted, a gland packing (54) which is twisted as shown in FIG. 25 is produced. In conventional art 2 above, when eight gland packing materials (50) are bundled and an eight-strand square-knitting process is conducted, for example, a gland packing (54) which is braided as shown in FIG. 26 is produced, and, when six gland packing materials (50) are bundled and a twisting process is conducted, a gland packing (54) which is twisted as shown in FIG. 27 is produced.
Each of the conventional gland packings (54) is provided by the expanded graphite tape (51) with properties which are preferable in sealing, and which are inevitable in a packing, such as the heat resistance, the compressibility, and the recovery property, and hence can seal a shaft seal part of a fluid apparatus while producing a high sealing property. Furthermore, metal wires have high bendability, and hence can cope with not only production of a gland packing (54) having a large diameter, but also that of a gland packing (54) having a small diameter, and has advantages such as excellent durability.
In order to produce any one of the conventional gland packing materials (50), however, knitting or other braiding of metal wires must be conducted by a knitting machine or a braiding machine. At this time, metal wires are subjected to braiding or the like by a knitting or braiding machine having a complicated structure. Therefore, high-speed production is hardly conducted, and the productivity is poor. Consequently, these gland packing materials (50) have problems in that their costs are high, and also the cost of the gland packing (54) is high. Moreover, the gland packing materials (50) have a poor shape-retaining property, thereby causing a possibility that expanded graphite may drop off during the braiding to lower the sealing property.
In the gland packing materials (50), the outer portion is reinforced by the knitted or braided member of metal wires. In the gland packing (54) which is produced by such a gland packing material (50), therefore, the reinforcing member (53) configured by a knitted or braided member of metal wires is in sliding contact with components of a fluid apparatus such as a pump shaft or a valve rod which rotates or axially slides, i.e., a counter member. At this time, there is a problem in that the reinforcing member (53) easily damages the counter member. Moreover, the reinforcing member (53) exhibits a high sliding resistance, and hence there is another problem in that the rotation performance or axial sliding performance of the counter member is lowered.
In order to solve these problems, it may be contemplated to use carbon fibers, and brittle fibers such as economical glass fibers, silica fibers, and ceramic fibers such as alumina and alumina-silica, as a reinforcing member which covers the cord-like member (52) of the expanded graphite tape (51) to apply external reinforcement. These carbon fibers and other brittle fibers can sufficiently withstand a braiding or twisting process in production of the gland packing (54), and has properties that, even when stranded, they are hardly broken.
In the case where the gland packing (54) is produced by the gland packing material (50) which is reinforced by such carbon fibers or brittle fibers, when a shaft seal part of a fluid-apparatus is sealed by the gland packing (54), it is expected that the counter member is not damaged, the sliding resistance is suppressed to a low level, the rotation performance or axial sliding performance of the counter member is improved, and the heat resistance is enhanced. In the case where economical brittle fibers such as glass fibers are used, particularly, it is expected to reduce the costs of the gland packing material (50) and the gland packing (54).
Unlike metal wires, however, carbon fibers and brittle fibers are low in toughness. Even when knitting or other braiding for externally reinforcing the expanded graphite tape (51) is tried, therefore, such fibers are broken. Consequently, it has been impossible to obtain the gland packing material (50) in which the expanded graphite tape (51) is externally reinforced by a reinforcing member configured by carbon fibers or brittle fibers.
The invention has been developed in view of the above-described circumstances. It is an object of the invention to provide a gland packing material having an external reinforcement structure which can be economically provided by improving the productivity, and the shape-retaining property is improved to enhance the sealing property, and a gland packing which is produced with using the gland packing material.
It is another object of the invention to enable external reinforcement by carbon fibers, whereby a counter member is prevented from being damaged in sealing, the sliding resistance is suppressed to a low level, and the heat resistance is enhanced.
It is a further object of the invention to enable external reinforcement by brittle fibers, thereby providing an economical gland packing material having an external reinforcement structure, and an economical gland packing which is produced with using the gland packing material.
It is a still further object of the invention to cope with production of gland packings in a wide range from a large diameter to a small diameter, and maintain an advantage of high durability.